Normally Job Administration SMS broadcasts will contain an $sms_body command to supply the message text. Individual lines of text can also be supplied on $sms_text commands. This text is always pre-processed at transmit time to expand variables, which should be introduced (by default) with the accent grave character (`).
The destination telephone number is given on an $sms_phone command from a list column. In most cases, you will also need to define SMS_ variables which will be specific to the SMS provider used.
For details of setting up SMS transmissions, see Sending SMS Messages.